1. Field of the Invention
The present invention relates to methods for separating mixed fatty acids and mixed tocopherols and sterols from complex mixtures. More specifically, the invention relates to a process for improving the yield of mixed fatty acids, tocopherols, and sterols separated from deodorizer distillates which are a byproduct of the edible oils and fats industries.
2. Description of Related Art
Deodorizer distillates are produced as a byproduct of the steam treatment-deodorization step in processes for producing edible oils and fats from vegetable materials. They are also produced as a byproduct of the production of oils and fats from animals. The distillates are comprised of fatty acids, oils, tocopherols, sterols, oxidation products, and miscellaneous other impurities, and are generally used for the production of oleo chemicals and other value added products.
Various methods for separating organic compounds from complex mixtures using urea as a complexing agent have been described in the related art. The crystalline complexes formed by urea and the selected organic compounds are inclusion complexes rather than true chemical reaction products. These complexes are unstable and, consequently, their components are easily regenerated by various means, including melting or dissolving of the urea lattice. Upon regeneration, urea and the selected organic compounds are separated.
In U.S. Pat. No. 2,520,716, a method is described for the extractive fractionation of organic compounds from complex mixtures by the use of agents such as urea and thiourea. One aspect of the method is based on the knowledge that urea selectively forms crystalline complexes with hydrocarbons having substantially a normal chain structure. Conversely, urea appears to be inert in this respect toward branched compounds such as isoparafins and most cyclic compounds such as aromatics and naphthenes. According to the method described in the patent, organic compounds are used which have partial solubility for the complex-forming agent, relatively low solubility (substantial immiscibility) for the complex forming hydrocarbons, and low solubility for the urea/hydrocarbon complex. These compounds are admixed with the urea composition to improve selectivity of the process for separating particular types of compounds.
U.S. Pat. No. 2,596,344 discloses a process for fractionating mixtures of vegetable oil acids or their derivatives. The invention is based on the discovery that mixtures of straight chain polar organic compounds may be effectively separated into fractions respectively richer and poorer in the chemically less saturated components by clathrate compound formation with urea. The invention involves the fractionation of mixtures of acids derived from naturally occurring fats and oils. According to the process, mixtures of naturally occurring glycerides are intentionally hydrolyzed or alcoholyzed in order to destroy the typical triglyceride structure and to leave the free acids or the esters of monohydric straight chain alcohols. Fatty acid mixtures are diluted with methyl isobutyl ketone and then stirred with saturated aqueous urea solutions. This forms a crystalline precipitate which is subsequently separated and dissolved to recover high-purity individual fatty acids.
According to U.S. Pat. No. 2,717,890, unsaponifiable materials present in tall oil are separated from the fatty acid fraction therein by mixing the tall oil with a concentrated aqueous solution of urea until a fatty acid complex is formed. The crystalline complex is filtered off and urea is leached out with water. The fatty acid fraction recovered is substantially free of unsaponifiable material.
U.S. Pat. No. 3,720,696 relates to a process for specifically extracting 9-hexadecenoic acid from fatty acid mixtures. According to Example 1, the fatty acid mixture was added to a solution of urea in methanol. Prior to addition, the solution was maintained at a temperature of less than 100.degree. C. Following addition, the solution was stirred and cooled to room temperature. The 9-hexadecanoic acid was ultimately recovered from the filtrate as a non-urea-addition product.
Urea is used in similar applications as a complexing agent in a process for isolating insect sex pheromones under U.S. Pat. No. 4,170,601; to purify eicosapentaenoic acid and its esters under U.S. Pat. No. 4,377,526 and to purify oleic acid under U.S. Pat. No. 4,601,856.
An improved process using urea for separating mixed fatty acids, tocopherols and sterols from deodorizer distillates has now been discovered. The process provides increased yields and reduced use of organic solvents.